Materials Science and Engineering, Cornell University, Ithaca, NY
Predictions of structure formation by computational methods have the potential to accelerate materials discovery and design. The self-assembly of nanocrystals into mesoscale superlattices provides a path to the design of materials with tunable electronic, physical and chemical properties for various applications. The self-assembly is controlled by the nanocrystal shape and ligand-mediated interactions between them. To understand this, it is necessary to know the effect of the ligands on the surface energies (which tune the nanocrystal shape), as well as the relative coverage of the different facets (which control the interactions). We will discuss how ab-initio calculations of surface and ligand-binding energies for PbSe nanocrystals predicts the equilibrium shape of the nanocrystals and a transition from octahedral to cubic when increasing the ligand concentration during synthesis. Our results furthermore suggest that the experimentally observed transformation of the nanocrystal superlattice structure from fcc to bcc is caused by the preferential detachment of ligands from particular facets, leading to anisotropic ligand coverage.
 C.R. Bealing, W.J. Baumgardner, J.J. Choi, T. Hanrath, and R. G Hennig; ACS Nano (2012)
 J.J. Choi, C.R. Bealing, K. Bian, K.J. Hughes, W. Zhang, D.-M. Smilgies, R.G. Hennig, James R. Engstrom, and Tobias Hanrath; J. Am. Chem. Soc. 133, 3131 (2011)